Method and an apparatus for severing or damaging unwanted plants

ABSTRACT

The present invention relates to a method and an apparatus capable of severing or damaging unwanted plants without using herbicides. The present invention relates in particular to an apparatus and a method for differentiating between different types of plants to allow identification of, and thus selective elimination or treatment of, individual plants. According to the present invention, the positioning of and the output power of at least one light generating means is controlled on the basis of information from an image recognition system which is capable of differentiating beween different plants.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/DK99/00405 which has an Internationalfiling date of Jul. 15, 1999, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for severingor damaging an unwanted plant by e.g. combining an optical imagerecognition system capable of differentiating between different types ofplants and a light generating means for exposing the plant toelectromagnetic radiation.

DESCRIPTION OF RELATED ART

In U.S. Pat. No. 5,296,702, a system is provided for plant recognition.The system disclosed in U.S. Pat. No. 5,296,702 comprises a targetingsystem for applying herbicides to individual plants so as to reduce theuse of herbicides. The system is capable of differentiating betweendifferent plants so that only a predetermined type of plants, e.g. anunwanted plant, will be exposed to herbicides.

A disadvantage of the system disclosed in U.S. Pat. No. 5,296,702 isthat the use of herbicides is not avoided.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and anapparatus capable of severing or damaging unwanted plants without usingherbicides.

In accordance with the present invention, an apparatus and a method areprovided for differentiating between different types of plants to allowidentification of, and thus selective elimination or treatment of,individual plants. In the present invention, the positioning of and theoutput power of at least one light generating means is controlled on thebasis of information from an image recognition system which is capableof differentiating between different plants.

The image recognition system provides an output signal for eachdifferent plant being imaged and identified. A controller analyses theoutput signal from the image recognition system, and assuming the imagedplant is a utility plant, no action is taken with respect to the plant.In the case where an unwanted plant has been identified, informationrelating to the position, and optionally the type of plant, istransmitted to a control system. The control system directs at least onelight beam, such as with a plant-dependent intensity, toward theunwanted plant in order to damage or actually sever the plant.Alternatively all plants not recognised as utility plants may beradiated.

An advantage of the present invention is that the use of herbicides iscompletely avoided.

A further advantage of the present invention is related to the fact thatit may operate under a wide variety of weather conditions includingwindy conditions, bright sunlight, artificial illumination or even totaldarkness. Especially the operability under windy conditions is anadvantage, since the use of herbicides under such conditions normallyresults in over—spay.

The present invention brings the farmer close the goal where:

no unwanted plants are over-looked, and

the use of herbicides is completely avoided

More specifically, in a first aspect the invention relates to anapparatus for severing or damaging plants, the apparatus comprising:

means for generating image data representing at least part of a plant,

means for analysing the image data and for determining whether the plantis one of a number of predetermined plants or types of plants, and, fromthat determination, whether the plant is to be severed or damaged,

severing or damaging means adapted to generate and direct a beam ofelectromagnetic radiation toward the plant in a manner so that at leastpart of the plant is severed or damaged.

As will be clear from the following, it may be over-kill to actuallyfully sever the unwanted plants, as a thermal damaging thereof mayretard the growth sufficiently for the utility plants to “out grow” theunwanted plants and thereby prevail. Thermal damaging may be a localheating of a sufficiently large or vital part of the plant. A vital partof the plant is the stem, and a local heating—such as one leading tocell destruction—of a part thereof will prevent or reduce the liquid ledfrom the root to the leaves which again will kill or retard the plant.This will be described in more detail further below.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE shows the apparatus for severing or damaging plants.

In the present context, a predetermined plant or a predetermined type ofplant may be typical weeds. However, for use in specific crops,different plants or types of plants not normally considered as weeds maybe unwanted and required removed in order for the actual plants of thecrop to prevail. Therefore, the plants or types of plants may very welldiffer depending on the actual plants that are desired on the ground.

Alternatively, the predetermined plants or types of plants may be theactual utility plants desired on the ground. In that situation, plantsnot falling into that category may be taken as unwanted and soughtdamaged or severed.

In order for the apparatus to be able to cover more ground than thatanalysed in a stationary image taken by the image generating means, itis preferred that the apparatus further comprises means for translatingor moving the generating means and the severing or damaging means alonga surface. Normally, this surface will be the surface of the ground or afield where utility plants are grown and where e.g. weeds are to beremoved at least during germination and sprouting until the leaves ofthe utility plants are sufficiently large.

In this manner, the apparatus or parts thereof will move through thefield and deal with the unwanted plants therein area by area.

Often, in the fields, the utility plants are positioned at predeterminedpositions in order for the field to be optimally used and in order toensure that each utility plant has sufficient space. Naturally, thisknowledge may be used by the analysing system in that e.g. plantsoutside these predetermined positions may simply be determined asunwanted plants and therefore severed or damaged. Otherwise, theanalysing system may use a parameter relating to the distance from aplant being analysed to one or more of the predetermined positions (withsuitable tolerances)—the farther away, the larger a possibility of theplant being analysed being an unwanted plant.

Also or optionally, the apparatus may further comprise:

means for determining a relative position of the severing and damagingmeans, the plant to be severed or damaged, and one or more other plantsin the image data and which are not to be damaged or severed,

means for determining a relative position of the severing or damagingmeans, the plant to be severed or damaged, and the one or more otherplants where an at least substantially straight line is present betweenthe severing or damaging means and the plant, the line not intersectingthe other plants to any significant degree.

As the severing or damaging means operate using electromagneticradiation, no utility plants should be in the way when irradiating theunwanted plant. However, a slight irradiation of a utility plant may betolerated. Also, it should be remembered that especially when the imagedata relate to an image taken from above and when the radiation isdirected substantially horizontally, parts of the image data relating toleaves will, in fact, not be irradiated due to the stem of the plantbeing the target and not being in that position.

Preferably, the determined relative position is also one wherein adistance from the plant and each of the one or more plants, in adirection from the severing or damaging means to the plant, exceeds apredetermined distance. This predetermined distance may be determined sothat radiation impinging on a plant at that distance will not or onlyslightly damage that plant. Normally, this distance will depend on theintensity and degree of focussing of the beam.

Also, the actual direction may “vary” slightly, if the beam isscanned—and in accordance with the width of the beam, if this is widecompared to the width of the impinged part of the plant.

Preferably, the moving means are adapted to move the severing ordamaging means in order to obtain the determined relative position, andpreferably the severing or damaging means are adapted to direct the beamtoward the plant—in order for the severing or damaging means to sever ordamage the plant and not to any significant degree the other plants.

It should be noted that the actual plant to be severed or damaged needsnot be represented in the image data at the point in time for severingor damaging, as the apparatus may comprise means for determining thespeed, direction, etc. required in order to determine when thepredetermined position has been reached.

When the movement of the apparatus or parts thereof is along apredetermined direction or path, preferably the predetermined positionis selected (if several positions are possible) along that direction orpath.

In order to obtain a sufficient severing or damaging of the plant, theintensity of the beam should be selected in accordance with the timeavailable for the irradiation. Preferably, a relatively large part ordiameter of the plant—and especially the stem thereof—is irradiated anddamaged/severed. If the beam has a width comparable to that of theirradiated part of the plant, a stationary beam may accomplish that. Ifa higher beam intensity is required, it is preferred that the means fordirecting the beam toward the plant are adapted to scan the beam over apredetermined area. In this manner, a smaller energy may be required atthe expense, of a larger irradiating/scanning time.

Preferably, in order to optimally damage the unwanted plant, the stemthereof is irradiated, whereby the scanning needs only encompass theposition of the stem. Naturally, this scanning brings about the“variation” in the above direction when ensuring that no utility plantsare damaged by the scanning.

It has been found that different unwanted plants require differentintensities in order to be sufficiently damaged or actually severed.However, generally, when the beam is focussed to a beam waist of 10 μmto 1 mm, such as 100 μm to 500 μm, has been found sufficient to sever ordamage most unwanted plants sufficiently. Consequently, the severing ordamaging means may comprise means for setting the size and position ofthe beam waist as well as the actual intensity of the beam depending oninformation from the generating means as to the distance to the unwantedplant, the position thereof (such as of the stem thereof), and as to thetype and/or size thereof.

Also, it is contemplated that different unwanted plants or types ofplants may have different damaging or severing characteristics so thatit may be preferred that these are irradiated with differentwavelengths.

Preferably, the generating means are adapted to generate image datarelating to an image of the plant from a direction at least partly fromabove the plant, and the severing or damaging means are adapted todirect the beam along a direction being at least substantiallyhorizontal. In this manner, the image data comprise data relating to theleaves of the plants while the radiation may be directed toward thestems thereof.

Due to the fact that the stem is normally the most vulnerable part ofthe plant—or the easiest place to severely damage or sever the plant,and that the image data preferably relate to the leaves thereof, theanalysing means are preferably adapted to estimate from the image dataof the plant a position of a stem of the plant to be severed or damaged,and wherein the severing or damaging means are adapted to direct thebeam toward the estimated position of the stem—optionally with ascanning thereof.

Naturally, a number of ways exist of determining whether image datarelate to one plant or type of plant or another. However, preferably theanalysing and determining means are adapted to:

from the image data, deriving one or more features relating to a shape,structure, and/or colour of at least part of a leaf of the plant,

determine, on the basis of the derived feature(s), whether the plant isone of the number of predetermined plants or types of plants.

For example, a feature may be derived from the shape or pattern of theouter contour of the leaf or the structure of the midribs and veins ofthe leaf. Also the size thereof or the relative positions of differentleaves of the same plant may provide information as to the type thereof.

In a second aspect, the invention relates to a method of severing ordamaging plants, the method comprising:

generating image data representing at least part of a plant,

analysing the image data and determining whether the plant is one of anumber of predetermined plants or types of plants, and, from thatdetermination, whether the plant is to be severed or damaged, and

generating and directing a beam of electromagnetic radiation toward theplant in a manner so that the at least part of the plant is severed ordamaged.

Preferably, the generating means and the severing or damaging means aremoved or translated along a surface.

As described above, the method further preferably comprises:

determining a relative position of the severing and damaging means, theplant to be severed or damaged, and one or more other plants in theimage data and which are not to be damaged or severed,

determining a relative position of the severing or damaging means, theplant to be severed or damaged, and the one or more other where an atleast substantially straight line is present between the severing ordamaging means and the plant, the line not intersecting the other plantsto any significant degree.

Most often, the relative position is also one wherein a distance fromthe plant and each of the one or more plants, in a direction from thesevering or damaging means to the plant, exceeds a predetermineddistance.

Therefore, normally, the moving means would then move the severing ordamaging means in order to obtain the determined relative position, andwherein the severing or damaging means direct the beam toward the plant.

Due to the power requirements of such a system, the step of directingthe beam toward the plant preferably comprises scanning the beam over apredetermined area.

As described above, the generating means may generate image datarelating to an image of the plant from a direction at least partly fromabove the plant, and wherein the severing or damaging means direct thebeam along a direction being at least substantially horizontal.

Also, the analysing means would normally estimate from the image data ofthe plant, a position of a stem of the plant to be severed or damaged,and the severing or damaging means would direct the beam toward theestimated position of the stem.

Even further, the analysing and determining means may further performthe step of:

from the image data, derive one or more features relating to a shape,structure, and/or colour of at least part of a leaf of the plant,

determine, on the basis of the derived feature(s), whether the plant isone of the number of predetermined plants or types of plants.

The invention will be more fully understood in light of the followingdetailed description of preferred embodiments of the invention. Thefollowing description is meant to be illustrative only and not limiting.Alternative embodiments of the invention will be obvious in view of thefollowing disclosure.

The preferred image recognition system comprises an optical imagingsystem for projecting an image onto an array of photosensitive elements,such as a charge coupled device (CCD), so as to generate an electricalrepresentation of the object to be imaged. The image recognition systemis mounted to provide a top-down view of the object to be imaged.

The electrical representation of the object is analysed by a controllerelectrically linked to the photosensitive elements. For identificationpurposes, the controller is also linked to a storage unit whereinformation relating to the relevant plants is stored. The imagerecognition system may operate in one of two modes:

1. In the first mode of operation, the image recognition system matchesthe plants in the image with information stored in the storage unit toidentify unwanted plants, where the apparatus subsequently severs ordamages these plants.

2. In a second and different mode, the image recognition systemidentifies utility plants by comparing the imaged plants withinformation stored in the storage unit. The apparatus subsequentlyservers or damages the other plants in the image.

In the process of recognising plants, the edge structure of leaves maybe used. Alternatively, the shape of leaves and the fine structure ofleaves may also be used in the identification process of a specificplant. Finally, the colour of leaves may be used in the identificationof the plants.

It is evident that identification of a given plant from its colour maybe problematic, since the colour of the reflected light from the leavesis dependent on the colour of the incident light, i.e. the colour of thelight reflected from a leaf is different in daylight compared to thecolour reflected by the same leaf in artificial illumination. Thus,identification of plants via colour is preferably performed usingartificial illumination. Otherwise, a daylight calibration would bepreferably on the basis of which the apparatus will be able to adapt tochanges in the illumination.

Both visible light, near-infra red (NIR) light and ultraviolet light maybe used as artificial illumination. If a silicon based CCD is used, bothNIR light and visible light may be detected. Thermal imaging may provideadditional information making the identification of plants morereliable.

As mentioned above, one manner of identifying an unwanted plant may beseen from U.S. Pat. No. 5,296,702.

When an unwanted plant has been positively identified by the imagerecognition system and the position of its stem has been determined, asignal is transmitted to the control system so as to direct a light beamin the direction of the unwanted plant in order to server or damage apart of the unwanted plant.

Light generating means may be gas laser, such as argon-ion lasers orpreferably CO₂ lasers. However, more suitable may be solid state lasers,such as semiconductor lasers or a Nd: YAG laser. Such semiconductorlasers may be GaAs-based or GalnP-based lasers. The laser beam may beeither a continuum wave or pulsed laser beam where at least one laserpulse is transmitted towards a specific plant. Wavelengths the rangefrom ultra-violet (190 nm) to the far-infra red (10600 nm) may beapplied. Especially at the shorter wavelengths, photo-chemistry islikely to take part in the damaging or severing of the plant.

When the data relating to the plants relate to the leaves thereof, theoptical axes of the generated light beams are preferably at an angle tothe optical axis of the image recognition system. However, in analternative embodiment, the plants may be identified and classified bydata relating to their stems. In that situation, also the imagerecognition system may be directed at least substantially horizontally.

The choice of radiation wavelength may be related to the choice ofmechanism responsible for the damage or severing of an unwanted plant.In the infrared, this mechanism may be a local thermal process in thestem of the unwanted plant mainly due to heating of water present in thestem. In order to obtain a sufficient power density, the laser beam isfocussed to a spot size with a diameter smaller than 1 mm, such as 100to 500 μm.

In the infrared region, the water in the stem may be efficiently heatedby selecting a radiation wavelength close to the water absorption peaks.Water absorption peaks are distributed over a large range. The rangefrom 800 nm to 10600 nm exhibits a plurality of absorption peaks. Bymatching the radiation wavelength to one of the water absorption peaks,the efficiency of especially the initiation of a thermal process issignificantly increased.

Also, a photochemical process may be used for damaging the plant.

The positioning of the laser beam is preferably performed using movablemirrors. The movement may comprise a rotation or translation or both, soas to direct the laser in a direction determined by the imagerecognition system.

Suitable means for provided movements of mirrors may be electricalmotors, such as servo motors or stepping motors, or piezo-electricelements.

The depth resolution of the laser system is determined by the length ofthe beam waist. Movable optical elements, such as lenses, mirrors, orprisms, may be applied in order to be able to adjust the width andlength of the beam waist for different purposes.

The width of the beam waist is adjusted so as to obtain the requiredpower density for a specific application. It is estimated that therequired exposure of the plant is in the range of 0.01-25 J/mm², such as0.1-1 J/mm².

Adjustment of the length of the beam waist enhances the selectivity ofthe system, since the power density is significantly increased withinthe beam waist. This can be used in the situation where a unwanted plantor a utility plant has been identified, and its position has beendetermined by the image recognition system. The beam waist of the laserbeam is then adjusted so that the position of the identified an unwantedplant falls within the beam waist.

By moving the optical elements, the beam waist may be moved along thebeam path, whereby selectivity along the beam path is achieved. This,however, may not be required where the distance between e.g. the rows ofutility plants is well defined compared to the focal depth.

The longer the beam waist the longer the distance will be within whichplants will be damaged or severed. If the optics so allow, it may bepreferred that the beam waist is quite short—but positioned at the rightdistance from the laser—so that the beam disperses a short distancetherefrom to a degree so that other plants in that direction are notaffected by the beam. Also, the more focussed the beam, the lower energyis required in order to damage or sever the plant.

When an unwanted plant has been identified by the image recognitionsystem, the exact position of the stem is not always known since leavesmay limit the top field of view of the image recognition system.Therefore, if the stem cannot be precisely located, the imagerecognition system defines an area, wherein the stem is located within apredetermined accuracy. The laser beam may then firstly be directedtoward the centre of this area and subsequently scanned horizontally tocover the whole area.

This determination of the position of the stem may most easily be chosenas a middle area of the area covered by leaves of the plant. A moresophisticated method is one taking into account that most leaves areelongate and connected to the stem at one end. Thus, by analysing thedirection of the leaves may provide a better estimate of the position ofthe stem. The smaller an area within which the stem should bepositioned, the more precise and the quicker a severing or damaging isobtained.

When using high power densities, the stem of the weed breaks when thelaser beam hits the stem. After exposure, the image recognition systemmay then return the to the site of the plant to confirm whether thelight exposure was sufficient for severing. If the stem is broken, nofurther action is taken in respect to this specific plant. If the lightexposure had insufficient impact on the plant, steps toward anadditional exposure is taken. After an additional exposure, the imagerecording system checks whether the additional exposure had sufficientimpact on the plant.

A further advantage of the present invention is concerned with the factthat the image recognition system may delay the light exposure until thelight path from the position of the laser to the position of the plantis free.

Due to the fact that the image data will relate to a two-dimensionalarea, the identified unwanted plant may be positioned so thatirradiation from the actual position of the laser is not possible, as itmight also damage a utility plant in the process. This may be due to theutility plant being positioned between the laser and the unwanted plantor that it is positioned too close to (such as directly behind) theunwanted plant in order to ensure that it is not irradiated duringscanning of the laser or due to the unwanted plant severing and thelaser beam travelling past it and on to the utility plant.

Thus, irradiation of the unwanted plant is obtained by moving the laserin relation to the unwanted plant and the utility plant(s) so that thelaser may directly irradiate the unwanted plant. Irradiation requires adirect open path from the laser to the unwanted plant. However, it alsorequires a certain space directly and substantially directly behind theunwanted plant in order to give space to the scanning laserbeam—optionally also directly behind the position of a severed unwantedplant.

This relative positioning may be determined from the image data. Itshould be noted that the unwanted plant needs not be in the image dataat the point in time of irradiation, if the apparatus comprises meansfor determining when the relative positioning has been obtained.

This situation may be seen if, e.g., the unwanted plant is only“accessible” from a direction opposite to those from which the laser isadapted to irradiate the plant. In that situation, a second laser may beprovided which is able to irradiate the plant from a differentdirection. Also, this may provide an irradiation from two sides ofunwanted plants that will further enhance the probability ofsufficiently damaging or severing the unwanted plants.

During operation, the present invention may be mounted on a tractor thatis man-driven through the field where growth of weed is to becontrolled. In another configuration, the present invention may bemounted on a computer-controlled vehicle, such as one navigating via theGlobal Positioning System (GPS) or along rows of plants in the field.

What is claimed is:
 1. An apparatus for severing or damaging plants, theapparatus comprising: means for generating image data representing atleast part of a plant, means for analyzing the image data and fordetermining whether the plant is one of a number of predetermined plantsor types of plants, and, from that determination, whether the plant isto be severed or damaged, severing or damaging means adapted to generateand direct a beam of electromagnetic radiation toward the plant in amanner so that at least part of the plant is severed or damaged by theeffect of the electromagnetic radiation, wherein the analyzing means areadapted to estimate from the image data of the plant a position of astem of the plant to be severed or damaged, and wherein the severing ordamaging means are adapted to direct the beam of electromagneticradiation toward the estimated position of the stem.
 2. An apparatusaccording to claim 1, further comprising means for translating or movingthe generating means and the severing or damaging means along a surface,such as the ground or a field.
 3. An apparatus according to claim 2,further comprising means for determining a relative position of thesevering and damaging means, the plant to be severed or damaged, and oneor more other plants in the image data and which are not to be damagedor severed, and means for determining a relative position of thesevering or damaging means, the plant to be severed or damaged, and theone or more other plants where an at least substantially straight lineis present between the severing or damaging means and the plant, theline not intersecting the other plants to any significant degree.
 4. Anapparatus according to claim 3, wherein the relative position is alsoone wherein a distance from the plant and each of the one or more otherplants, in a direction from the severing or damaging means to the plant,exceeds a predetermined distance.
 5. An apparatus according to claim 3,wherein the moving means are adapted to move the severing or damagingmeans in order to obtain the determined relative position, and whereinthe severing or damaging means are adapted to direct the beam toward theplant.
 6. An apparatus according to claim 1, wherein the means fordirecting the beam toward the plant are adapted to scan the beam over apredetermined area.
 7. An apparatus according to claim 1, wherein thegenerating means are adapted to generate image data relating to an imageof the plant from a direction at least partly from above the plant, andwherein the severing or damaging means are adapted to direct the beamalong a direction being at least substantially horizontal.
 8. Anapparatus according to claim 1, wherein the analyzing and determiningmoans arc adapted to: from the image data, deriving one or more featuresrelating to a shape, structure, and/or color of at least part of a leafof the plant, and determine, on the basis of the derived feature(s),whether the plant is one of the number of predetermined plants or typesof plants.
 9. A method of severing or damaging plants, the methodcomprising: providing means for generating image data representing atleast part of a plant, providing means for analyzing the image data anddetermining whether the plant is one of a number of predetermined plantsor types of plants, and, from that determination, whether the plant isto be severed or damaged, providing means for generating and directing abeam of electromagnetic radiation toward the plant in a manner so thatat least a part of the plant is severed or damaged by the effect of theelectromagnetic radiation, wherein the provided analyzing means estimatefrom the image data of the plant, a position of a stem of the plant tobe severed or damaged, and wherein the severing or damaging means directthe beam of electromagnetic radiation toward the estimated position ofthe stem.
 10. A method according to claim 9, further comprisingtranslating or moving the generating means and the severing or damagingmeans along a surface, such as the ground or a field.
 11. A methodaccording to claim 10, further comprising determining a relativeposition of the severing and damaging means, the plant to be severed ordamaged, and one or more other plants in the image data and which arenot to be damaged or severed, and determining a relative position of thesevering or damaging means, the plant to be severed or damaged, and theone or more other plants where an at least substantially straight lineis present between the severing or damaging means and the plant, theline not intersecting the other plants to any significant degree.
 12. Amethod according to claim 11, wherein the relative position is also onewherein a distance from the plant and each of the one or more plants, ina direction from the severing or damaging means to the plant, exceeds apredetermined distance.
 13. A method according to claim 11, wherein themoving means move the severing or damaging means in order to obtain thedetermined relative position, and wherein the severing or damaging meansdirect the beam toward the plant.
 14. A method according to claim 9,wherein the step of directing the beam toward the plant comprisesscanning the beam over a predetermined area.
 15. A method according toclaim 9, wherein the generating means generate image data relating to animage of the plant from a direction at least partly from above theplant, and wherein the severing or damaging means direct the beam alonga direction being at least substantially horizontal.
 16. A methodaccording to claim 9, wherein the analyzing and determining meansfurther perform the step of: from the image data, derive one or morefeatures relating to a shape, structure, and/or color of at least partof a leaf of the plant, and determine, on the basis of the derivedfeature(s), whether the plant is one of the number of predeterminedplants or types of plants.
 17. An apparatus according to claim 1,wherein the beam of electromagnetic radiation comprises a laser beam.18. A method according to claim 9, wherein the beam of electromagneticradiation comprises a laser beam.